User operated drug delivery devices are as such known in the prior art. They are typically applicable in circumstances, in which persons without formal medical training, i.e. patients, need to administer an accurate and predefined dose of a medicinal product, such as heparin or insulin. In particular, such devices have application, where medicinal product is administered on a regular or irregular basis over a short term or long-term period.
In order to accommodate with these demands, such devices have to fulfil a number of requirements. First of all, the device must be robust in construction, yet easy to use in terms of handling and in understanding by the user of its operation and the delivery of the required dose or medicament. The dose setting must be easy and unambiguous. Where the device is to be disposable rather than reusable, the device should be inexpensive to manufacture and easy to dispose (preferably being suitable for recycling). To meet these requirements, the number of parts required to assemble the device and the number of material types the device is made from need to be kept to a minimum.
Document U.S. Pat. No. 7,396,347 B2 discloses for instance an injector device for a syringe container with a piston rod arrangement operable to displace a moveable wall of the container in forward direction.